A method for switching a mode of resources allocated from a broadband wireless access system to a mobile station will hereinafter be described in detail. Switching the mode of resources indicates the switching between a normal sub-channel and a band AMC sub-channel. The normal sub-channel may be composed of a distributed sub-carrier permutation, and the band AMC (Adaptation modulation Coding) sub-channel may be composed of an adjacent sub-carrier permutation. The above-mentioned mode switching request operation may use messages or may use channel quality information channel (CQICH) of 6 bits.
FIG. 1 is a flow chart illustrating a general mode switching process from a normal sub-channel to a band AMC sub-channel.
Referring to FIG. 1, a mobile station (MS) may determine to request the switching to the band AMC sub-channel according to communication environments. In this case, the mobile station (MS) transmits an REP-RSP message including measurement values of 4 or 5 bands (hereinafter referred to as the best bands), each of which has a high CINR (Carrier to Interference and Noise Ratio), to a base station (BS) in order to perform the switching from the normal sub-channel to the band AMC sub-channel. In this case, the mobile station (MS) may establish a predetermined band AMC transition delay time, and may transmit the REP-RSP message during the established band AMC transition delay time at step S101.
The mobile station (MS) periodically transmits differential CINRs of best bands to the base station (BS) over the CQICH at step S102.
The base station (BS) having received the REP-RSP message checks the CINRs of the best bands contained in the REP-RSP message, and may approve the MS request of switching to the band AMC mode at step S103.
The base station (BS) transmits a DL-MAP message acting as a control message to the mobile station (MS), such that it informs the MS of band AMC allocation information of an MPDU to be transferred to the mobile station (MS) using the DL-MAP message at step S104.
However, if the mobile station (MS) did not receive the DL-MAP message from the base station (BS) within the band AMC transition delay time (i.e., if the MS was timed out), it recognizes the occurrence of a failure in the switching to the band AMC mode at step S105.
The mobile station (MS) recognizes that the switching to the band AMC mode has failed, such that it transmits a CNIR of a normal sub-channel to the base station (BS) using the latest-received CQICH allocation information element (IE) at step S106.
However, the base station (BS) has been switched to the band AMC mode by a request of the mobile station (MS), such that CQICH information transferred from the mobile station (MS) may be invalid.
If the base station (BS) requests the mode switching to the band AMC sub-channel, it further includes only the above process for transmitting the REP-REQ message to the mobile station (MS) in all the processes of the MS which requests the mode switching. So, all the BS processes except for the above transmission of the REP-REQ message are equal to those of the mobile station (MS).
FIG. 2 is a flow chart illustrating a general mode switching process from the band AMC sub-channel to the normal sub-channel.
Referring to FIG. 2, the mobile station (MS) may request the switching from the band AMC channel to the normal sub-channel according to communication environments. Therefore, the mobile station (MS) transmits the REP-RSP message including the CINR of the normal sub-channel to the base station (BS) at step S201.
In this case, the mobile station (MS) may transmit differential CINRs of the best bands to the base station (BS) over the CQICH at step S202.
The base station (BS) having received the REP-RSP message checks the CINR of the normal sub-channel contained in the REP-RSP message, and then approves the MS request of switching to the normal AMC mode at step S203.
In this case, the base station (BS) transmits the UL-MAP message acting as a control message, which includes a CQICH allocation IE indicating the switching to the normal sub-channel, to the mobile station (MS) at step S204.
However, if the mobile station (MS) did not receive the UL-MAP message from the base station (BS) at step S204, it recognizes the occurrence of a failure in the switching to the normal mode at step S205.
Although the base station (BS) has informed the mobile station (MS) of allocation information of a normal channel of the MPDU to be transferred to the mobile station (MS) using the DL-MAP message at step S206, the mobile station (MS) transmits differential CINRs of the best bands over the CQICH of the prior band AMC at step S207. However, the base station (BS) has been switched to the normal sub-channel mode by a request of the mobile station (MS), such that CQICH information transferred from the mobile station (MS) may be invalid.
In other words, FIGS. 1 and 2 assumes that the mobile station (MS) does not receive an MAP IE message although the base station (BS) has approved the mode switching using the MAP IE message acting as the control message. If the mobile station (MS) did not receive the MAP IE message acting as the control message, the mobile station (MS) and the base station (BS) are operated in different modes, such that unexpected problems may occur.